In my own headcanon, I like to believe the whole story of the
novella about Mapleshade took place about 15 years before Bluestar
is born. Reasons why I think that?

Well, as we know from Crookedstar’s Promise, Reedshine is
Shellheart’s grandmother and I can assume that Hailstar succeeded
Darkstar as leader. Shellheart is, I am pretty sure, already a
senior warrior by the time Crookedkit is born - and from what I
understand, a senior warrior is on average at least 5 years old.
One of Reedshine’s kits - a.k.a. Shellheart’s mother - probably
lived to be an elder and died a few seasons before Crookedkit and
Oakkit were born. Then according to my timeline, Shellheart
might be older tha…